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Date: Mon, 9 Sep 2013 22:32:25 -0700
From: Eric Hodel <drbrain@...ment7.net>
To: Operating system distro security contacts <distros@...openwall.org>,
 "oss-security@...ts.openwall.com" <oss-security@...ts.openwall.com>
Subject: CVE-2013-4287 Algorithmic complexity vulnerability in RubyGems 2.0.7 and older

RubyGems validates versions with a regular expression that is vulnerable to
denial of service due to backtracking.  For specially crafted RubyGems
versions attackers can cause denial of service through CPU consumption.

RubyGems versions 2.0.7 and older, 2.1.0.rc.1 and 2.1.0.rc.2 are vulnerable.

Ruby versions 1.9.0 through 2.0.0p247 are vulnerable as they contain embedded
versions of RubyGems.

It does not appear to be possible to exploit this vulnerability by installing a
gem for RubyGems 1.8.x or 2.0.x.  Vulnerable uses of RubyGems API include
packaging a gem (through `gem build`, Gem::Package or Gem::PackageTask),
sending user input to Gem::Version.new, Gem::Version.correct? or use of the
Gem::Version::VERSION_PATTERN or Gem::Version::ANCHORED_VERSION_PATTERN
constants.

Notably, users of bundler that install gems from git are vulnerable if a
malicious author changes the gemspec to an invalid version.

The vulnerability can be fixed by changing the first grouping to an atomic
grouping in Gem::Version::VERSION_PATTERN in lib/rubygems/version.rb.  For
RubyGems 2.0.x:

  -  VERSION_PATTERN = '[0-9]+(\.[0-9a-zA-Z]+)*(-[0-9A-Za-z-]+(\.[0-9A-Za-z-]+)*)?' # :nodoc:
  +  VERSION_PATTERN = '[0-9]+(?>\.[0-9a-zA-Z]+)*(-[0-9A-Za-z-]+(\.[0-9A-Za-z-]+)*)?' # :nodoc:

For RubyGems 1.8.x:

  -  VERSION_PATTERN = '[0-9]+(\.[0-9a-zA-Z]+)*' # :nodoc:
  +  VERSION_PATTERN = '[0-9]+(?>\.[0-9a-zA-Z]+)*' # :nodoc:

This vulnerability was discovered by Damir Sharipov <dammer2k@...il.com>

The above information is also posted at:

http://blog.rubygems.org/2013/09/09/CVE-2013-4287.html

Patches were committed for:

RubyGems 2.1.0.rc.2, released as RubyGems 2.1.0:

https://github.com/rubygems/rubygems/commit/938a7e31ac73655845ab9045629ff3f580a125da

RubyGems 2.0.7, released as RubyGems 2.0.8:

https://github.com/rubygems/rubygems/commit/b9baec03145aed684d1cd3c87dcac3cc06becd9b

RubyGems 1.8.25, released as RubyGems 1.8.26:

https://github.com/rubygems/rubygems/commit/ed733bc379d75620f5be4213f89d1d7b38be3191

RubyGems 1.8.23, released as RubyGems 1.8.23.1:

https://github.com/rubygems/rubygems/commit/b697536f2455e8c8853cf5cf8a1017a36031ed67

The following program can be used to test if you are vulnerable to CVE-2013-4287:


require 'benchmark'
require 'rubygems'

valid = Benchmark.measure do
  Gem::Version.new '1.22.333.4444.55555.666666.7777777'
end

puts 'Valid version time:'
puts valid

invalid = Benchmark.measure do
  begin
    Gem::Version.new '1.22.333.4444.55555.666666.7777777.'
  rescue
  end
end

puts 'Invalid version time:'
puts invalid

n = (valid.real - invalid.real).abs

if 0.1 < n then
  puts 'You are vulnerable to CVE-2013-4287.'
else
  puts 'You are NOT vulnerable to CVE-2013-4287.'
end






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